Planting hole size and configuration

Planting
and establishing trees is all about managing air and moisture in the soil. Manage these correctly
and trees will grow quickly following planting. Four of the most common causes
of poor plant establishment are 1) planting too deeply,
2) under watering, 3) over watering and 4) over-mulching (See:over-mulching). Planting too deeply in compacted soil can also
lead to very slow root development. Each of these problems can lead to extensive
tree death, poor growth, or a slow decline after planting. If appropriate trees
are planted at the right depth and they are irrigated properly, the planting
has a good chance of success. As simple as this appears to be, problems often
arise that lead to poor establishment or plant failure.

Before
digging the hole, 1) find the point where the top-most root emerges from the trunk (dig down next to the trunk to find this point), and 2) measure the distance between the top-most
root and the bottom of the root ball. Dig the hole slightly shallower
than this depth and as wide as possible (at least 1.5 times the width of the
ball-dig a much wider and shallower hole in compacted
soil). Do not dig the hole deeper than the root
ball. Consider drilling holes below the root ball in compacted soil or rock to encourage some deep roots.

When
planting on slopes set the tree so the top-most root in the ball on the
uphill side is about even with the soil. The
side of the root ball on the downhill side will be well above the surrounding
soil. Bring in enough soil to cover the sides of the root ball with soil. Apply
mulch to finish the planting job as shown in the diagram above.

When
planting in rock or very compacted soil break
up the substrate as best as possible to allow roots to anchor into the landscape (see:how to break up soil).
If this is not done, roots are likely to be very shallow and the tree may grow
poorly. Drilling holes in rock below the root ball might help encourage some deep roots that could help secure the tree in windy weather.